On 12/7/11 4:24 AM, Jim Thomson wrote:
> Date: Wed, 07 Dec 2011 00:19:21 -0500
> From: K8RI<K8RI-on-TowerTalk@tm.net>
> Subject: Re: [TowerTalk] Fwd: HDBX-48 figures for 90 mph zone
> To: towertalk@contesting.com
> Message-ID:<4EDEF759.7040005@tm.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> On 12/6/2011 11:13 PM, HansLG@aol.com wrote:
>>
>> In a message dated 12/6/2011 4:43:51 P.M. Eastern Standard Time,
>> w2lu@rochester.rr.com writes:
>>
>> As I recall wind pressure "on a flat surface" at 70 mph is 20.6 lbs/sq
>> ft.,
>> so if the tower is rated for
>> 18 sq ft at 70 mph, would it be too much of a stretch to say to the zoning
>> board that since wind pressure at 90 mph is 34 lbs/sq ft, by simple math,
>> the tower should be good for 10.9 sq ft at 90 mph ?
>> Gene / W2LU
>
> Regardless of wind area isn't there a boom length limitation on both the
> BX and HDBX series?
>
> 73
>
> Roger (K8RI)
>
> ## yes, I think they reduced it to just 10' years ago..and sales plummeted.
> Just fudge the ant wind load a bit, and perhaps 'take out' one section on
> paper.
> Then when u install it, add the extra section back in. IF you ever did hit
> it with
> a 90 mph wind, and a big ant, ur gonna be in for an eye opener. That thing
> about
> 70 mph = 20.6 sq feet. That's from 1976. 222- REV-D. It's now REV G !
> A Trylon T-500, 72' tall..is good for 22 sq feet @ 70mph....but only 6 sq feet
> at 100 mph. The tower itself will eat up all the windload. Toss in any
> ice,and
> you can kiss it goodbye. I wonder if the factory will even give you a
> windload
> rating for 90 mph ?
>
That's a tapered tower with a pretty large cross sectional area, of
angle iron. There's a pretty good chance that it would have an
available antenna area of less than zero with a 60% increase in wind
load. that square law thing really bites hard.
For those that are interested, the summarized analysis is in the back of
the BX manual
www.sufitchi.com/tower/manual.pdf
Gives cross sectional area for each section, heights of sections,
assumptions of strength for materials, etc.
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